There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Advancing perovskite solar cell technologies toward their theoretical power conversion efficiency (PCE) requires delicate control over the carrier dynamics throughout the entire device. By controlling the formation of the perovskite layer and careful choices of other materials, we suppressed carrier recombination in the absorber, facilitated carrier injection into the carrier transport layers, and maintained good carrier extraction at the electrodes. When measured via reverse bias scan, cell PCE is typically boosted to 16.6% on average, with the highest efficiency of ~19.3% in a planar geometry without antireflective coating. The fabrication of our perovskite solar cells was conducted in air and from solution at low temperatures, which should simplify manufacturing of large-area perovskite devices that are inexpensive and perform at high levels.

http://science.sciencemag.org/content/sci/345/6196/542.full.pdf

Interface engineering of highly efficient perovskite solar cells

A novel non-fullerene electron acceptor (ITIC) that overcomes some of the shortcomings of fullerene acceptors, for example, weak absorption in the visible spectral region and limited energy-level variability, is designed and synthesized. Fullerene-free polymer solar cells (PSCs) based on the ITIC acceptor are demonstrated to exhibit power conversion effi ciencies of up to 6.8%, a record for fullerene-free PSCs.

An electron acceptor challenging fullerenes for efficient polymer solar cells.

Continued advancements in organic materials have led to the development of organic devices that are thin, flexible, and lightweight and that can potentially be used as low-cost energy-conversion devices. While these devices have many advantages, the environmentally induced degradation of the active materials and the low-work-function electrodes remain a valid concern. Hence, many vacuum deposition processes have been applied to develop low-permeation barrier coatings. In this work, we present the results pertaining to the developed thin-film encapsulation. Multilayer encapsulation involves the use of or with parylene. The effective water vapor transmission rates were investigated using a Ca-corrosion test. The integration of the developed barrier layers was demonstrated by encapsulating pentacene/ solar cells, and the results are presented.

Fabrication and Characterization of High-Performance Thin-Film Encapsulation for Organic Electronics

Zeolites (nanoporous crystalline aluminosilicates) have important applications in catalysis and separations [1,2], and are also being considered for adsorption-based heating and cooling systems [3]. We are investigating the use of zeolite films in the fabrication of more efficient adsorption heat pumping and refrigeration systems that use water vapor as the working fluid. The thermal conductivity of the adsorbent is an important property affecting heat transfer in an adsorption heat pumping system. There are few reports (e.g. [4]) of the thermal conductivity of zeolites, which is measured by compacting the zeolite powder into a disk sample and using a model to extract the ‘intrinsic’ thermal properties. Another approach [5] relies on molecular dynamics simulation using parameterized force fields to predict the intrinsic thermal conductivity.Copyright © 2004 by ASME

Synthesis of Polycrystalline Zeolite Films and Thermal Conductivity Measurements by a 3-Omega Method

Beta-phase gallium oxide (β-Ga2O3) has garnered considerable attention for power devices due to (i) its large critical electric field strength and (ii) the availability of low cost/high quality melt-grown substrates, both of which are advantages over silicon carbide (SiC) and gallium nitride (GaN). However, because of the low thermal conductivity of β-Ga2O3, thermal management strategies at the device-level are required to achieve high-power operation. In this work, electrically identical MOSFETs (fixed current channel length) with varying spacings between the gate electrode and drain metal contact (thus, thermally different) have been fabricated, to study the effectiveness of heat extraction by the drain metal electrode. Results show that the topside features of lateral β-Ga2O3 MOSFETs are important in both electrical and thermal design perspectives.

The effectiveness of heat extraction by the drain metal contact of β-Ga 2 O 3 MOSFETs

Purpose




This paper aims to investigate the oxygen transport characteristics in the electrolyte membrane of proton exchange membrane fuel cell (PEMFC), in particular, the water content dependence and the microscopic view of the molecular transport.




Design/methodology/approach




Molecular dynamics simulation is used to examine the oxygen transport characteristics in the electrolyte membrane of PEMFC that we have experimentally observed in our previous study.




Findings




Molecular dynamics simulation well predicts the diffusion coefficient of oxygen in the membrane. It was found that the oxygen molecules have preference in their transport passage that governs the property.




Originality/value




First attempt is to theoretically examine the experimentally observed water uptake dependence of the oxygen diffusion coefficient in membrane and to explain the mechanism.

Molecular dynamics simulation of oxygen transport characteristics in the electrolyte membrane of PEMFC

This study explores the feasibility of single phase liquid channel cooling, pin fin cooling and spray cooling techniques for heat removal from a power electronic substrate. The substrate is formed using an AlN layer directly bonded to an AlSiC heat sink with a copper circuit layer. With a comparative assessment of the three cooling techniques using analytical modeling, the heat transfer coefficient and pressure drop in the package are optimized for a fixed coolant pumping power. Computational simulations of the three optimized geometries are performed to estimate the device temperatures and the maximum heat rates that can be dissipated with this pumping power. It is concluded that channel cooling yields the best thermal management performance and its use is recommended in the development of a packaged assembly.

Samuel Graham

Papers

Fabrication and Characterization of High-Performance Thin-Film Encapsulation for Organic Electronics

Synthesis of Polycrystalline Zeolite Films and Thermal Conductivity Measurements by a 3-Omega Method

The effectiveness of heat extraction by the drain metal contact of β-Ga 2 O 3 MOSFETs

Molecular dynamics simulation of oxygen transport characteristics in the electrolyte membrane of PEMFC

Efficient single-phase cooling techniques for durable power electronics module